1. Technical Field
The present invention generally pertains to an engine control system for governing the idle of an internal combustion engine. More particularly, but without restriction to the particular embodiment and/or use which is shown and described for purposes of illustration, the present invention relates to a stabilizing system used in conjunction with a torque based idle control system.
2. Discussion
The motor vehicle is an increasingly complicated, dynamically changing machine. In order to maximize performance and increase component durability, it is desirable to have the capability of controlling an engine to produce a specific engine flywheel torque. To accomplish this task, an accurate estimate of the engine's internal frictional loss must be calculated. In a torque based idle control system, the engine friction characterization is one of the primary requesters of torque. Because the engine friction estimate is a function of engine rotational speed and intake manifold pressure, small fluctuations in either component may cause similar fluctuations in the frictional loss estimate. Accordingly, an unstable idle may result due to the fluctuating, "noisy", estimate of the torque required to overcome friction.
During idle conditions, the driver's flywheel torque request is theoretically constant. Therefore, the desired torque during unloaded idle is equal to the friction torque estimate plus an idle control torque. The idle control torque is the additional torque required to idle the engine as determined by the idle speed control module. Instabilities can occur at idle because both the friction torque estimate and the idle control torque request vary with changes in engine speed and intake manifold pressure. De-coupling the friction torque estimate and the idle control torque requests at idle will allow for better idle control, especially in small displacement engines, resulting in greater customer satisfaction.